first of all thanks for your answer dear.
just one thing i didn't understand the first part because i am too beginner. can u explain me little more what is the ActionHook:ClientAreaPageCart and where should i put the php code ?

hi everyone , i want to remove password filed from the order form ! i can hide it but still the error will be there ! so client cannot submit the order. i want to know how can i remove completely ?
or please tell me how can do something to generate automatic password ? i mean after client order the password will be generate automatically and send it to the client email.
its very important for me